1. Field of the Invention
The present invention relates to a lithographic apparatus and a device manufacturing method.
2. Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. The lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs), flat panel displays, and other devices involving fine structures. In a conventional lithographic apparatus, a patterning means, which is alternatively referred to as a mask or a reticle, can be used to generate a circuit pattern corresponding to an individual layer of the IC (or other device), and this pattern can be imaged onto a target portion (e.g., comprising part of one or several dies) on a substrate (e.g., a silicon wafer or glass plate) that has a layer of radiation-sensitive material (e.g., resist). Instead of a mask, the patterning means can comprise an array of individually controllable elements that generate the circuit pattern.
In general, a single substrate will contain a network of adjacent target portions that are successively exposed. Known lithographic apparatus include steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion in one go, and scanners, in which each target portion is irradiated by scanning the pattern through the beam in a given direction (the “scanning” direction), while synchronously scanning the substrate parallel or anti-parallel to this direction.
In lithographic apparatus using a mask or reticle, in which the pattern is fixed, the image generated by the patterning means remains substantially constant over time, although it can degrade to some extent. Consequently, a manufacturer using such a lithographic apparatus has a relatively high level of confidence that the image being generated and projected onto a particular substrate is correct. However, when using an apparatus with an array of individually controllable elements as the patterning means, the pattern is dynamic and the manufacturer has less confidence that the image being produced and projected onto the substrate is correct until the exposed pattern on the substrate has been developed and the substrate has been inspected. Consequently, a greater number of more detailed inspections of the substrate must be performed after each pattern has been developed on the substrate and a larger amount of re-work can be required.
Therefore, what is needed is an arrangement that provides a manufacturer using a lithographic apparatus with a greater degree of confidence in accuracy and quality of an image being produced, enabling a reduction in inspection time of patterns after exposure and/or a reduction in an amount of re-work.